1. Field of the Invention
This invention has relation to a tool and a method for severing the thermoplastic covering or sheath around an electrical cable so that the severed piece of the sheath can be slid off of the cable to permit the wires inside to be separated, stripped at their ends, and connected to other electrical conductors. Such a tool and the use of such a method is particularly important to installers of original ROMAX or pbx or similar electrical cables in the construction of homes and industrial and commercial buildings where any saving of time during installation can be very important economically. Such a tool and method are also important to the home handyman and professional installer of new and supplemental wiring in existing structures.
2. Description of the Prior Art
Prior to the present invention, an installer would use a pocketknife or, more usually, a sheet rock knife also called a retractable razor blade holder, to slit the sheath longitudinally for the length that was to be removed. The sheath was then pulled off sideways from the paper wrapping and wires inside and a side cutting pliers was used to cut away the sheath and the paper wrappers so that the bare ground wire and the two or three insulated conductors were uncovered so that they could be attached to other electrical conductors in a junction box, in a switch box, or to some electrical appliance.
Many other devices for slitting the nonmetallic sheath longitudinally have been used. These include a device having a holder supporting a triangular blade which sticks down into the cable, hopefully between the insulated conductors in the cable, the installer wrapping his band around the cable and pulling the triangular blade the entire length of the cut and off of the end of the cable. Here again, the sheath must be peeled away and side cutting pliers used to cut it off where the slit was started. After this is accomplished, the paper wrapping was then cut off and only then were the insulated conductors available to be stripped at their own ends and so that they and the bare ground conductor were ready to be installed.
The difficulty with the use of a pocket knife or a sheet metal knife with a retractable razor edge point, and the trouble with the various stripping tools such as the one described immediately above is that sooner or later in a day work, the blade will knick one of the insultated conductors, leaving a weak point in the insulation. If this point happens to end up underneath the metallic clamp or adjacent a similar weak point in an adjacent insulated conductor, the insulation may eventually break down. In this instance, failure of the electrical circuit may be the least of the problems, and sparking and fire may be the worst.
In a preliminary search of this invention, the following U.S. patent documents were cited:
______________________________________ U.S. PATENT DOCUMENTS ______________________________________ D.247,268 2/78 Quenot 809,532 1/06 Schnackenberg 1,906,582 5/33 Gundlach 2,192,056 2/40 Watts 3,143,635 4/64 Hooker 3,968,670 7/76 Quenot 4,055,616 10/77 Keen et al ______________________________________
The concept of severing a cable sheath by burning or melting using a hot wire as an energy source is shown in the patents to Watts and to Keen. While these structures may be effective in factory installations, their bulk, weight, size, complexity and immobility render then ineffective for use in the installation of electrical cable "on the job" in the construction field. Also, the structures of Watts and Keen are much better adapted to be effective on round cables than on the oval shape cables of tow and three and more wires as used in construction. This is because of the difficulty of conforming the solid shape heating elements of Watts and Keen to the irregular shapes of cables used in construction.
A further difficulty with the teachings of the Watts and Keen patent grows out of the fact that there must be some substantial dwell time in the heating of the thermoplastic cable using these structures. Thus there is always a possibility that this heat will be transferred to the thermoplastic coatings on the interior insulated wires of a ROMAX cable, for example. Such heat can cause a weakening or a thinning of the insulation on the insulated wires and can cause troublesome weak spots in that insulation.
The Hooker patent discloses another thermal wire stripper which is, in the present context, subject to somewhat the same difficulties as those of Watts and Keen. It is more portable than Watts or Keen, but requires the availability of electrical power at the point of use.
The ancient patents to Scnackenberg and Gundlach simply disclose the use of cords to cut entirely through relatively soft materials. The patents are not believed to be particularly pertinent to the present invention.
The Quenot mechanical and design patents are cited to show key ring retaining and retrieving structures of a type which can be adapted for use in connection with the present invention. A number of different structures similar to those shown in the Quenot patents will be perfectly satisfactory for use in connection with the present invention; and the specific construction of the Quenot mechanical patent forms no part of the present invention per se.
The applicant and those in privity with him are aware of no prior art which is closer than that discussed above and are aware of no prior art which anticipates the claims made herein.